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Energy Spectra and High Frequency Oscillations in 4U 0614+091

Eric C. Ford·Philip Kaaret·Kaiyou Chen·Marco Tavani·Didier Barret·Peter Bloser·Jonathan Grindlay·B. Alan Harmon·William S. Paciesas·S. Nan Zhang
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Abstract

We investigate the behavior of the high frequency quasi-periodic oscillations (QPOs) in 4U 0614+091, combining timing and spectral analysis of RXTE observations. The energy spectra of the source can be described by a power law (alpha ~ 2.8) and a blackbody (kT ~ 1.5), with the blackbody accounting for 10 - 20% of the total energy flux. We find a robust correlation of the frequency, nu, of the higher frequency QPO near 1 kHz with the flux of the blackbody, F_BB. The slope of this correlation, dlog(nu)/dlog(F_BB), is 0.27 to 0.37. The source follows the same relation even in observations separated by several months. The QPO frequency does not have a similarly unique correlation with the total flux or the flux of the power law component. The RMS fraction of the higher frequency QPO rises with energy from 6.8 +- 1.5 % (3-5 keV) to 21.3 +- 4.0 % (10-12 keV). For the lower frequency QPO, however, it is consistent with a constant value of 5.4 +- 0.9 %. The results may be interpreted in terms of a beat frequency model for the production of the high frequency QPOs.

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Eric C. Ford, Philip Kaaret, Kaiyou Chen, Marco Tavani, Didier Barret, Peter Bloser, Jonathan Grindlay, B. Alan Harmon, William S. Paciesas, S. Nan Zhang. 1997-06-10. Energy Spectra and High Frequency Oscillations in 4U 0614+091. https://doi.org/10.1086/310827

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